Orthopaedic surgery often involves the installation of an implant. One example of such a procedure is the installation of a femoral implant in which the femoral head is replaced with a metallic implant having a ball and a stem that extends into the medullary canal of the femur for securing the implant. This procedure involves cutting through the femoral neck to remove the head and to obtain access to the medullary canal. After the cut through the femoral neck has been made, a broach or rasp is used to remove bone that has been exposed by the cut, in order to clear an opening to the medullary canal and to prepare the medullary canal itself so that the femoral implant can be installed.
Normally, the broach or rasp that is used to remove the bone comprises an elongate metallic body having a tip at one end and an outer surface that includes features such as ridges or teeth. The ridges or teeth can be engaged with the bone to be removed while the broach or rasp is moved back and forth, thereby to scrape the bone away. The tip of the device can be used as a pick, to chip bone away. These kinds of metallic broach or rasp comprise a monolithic metallic body. A disadvantage associated with broaches or rasps of this kind is that they are expensive to manufacture. Another disadvantage is that they are typically very heavy, which can make them difficult for a surgeon to manipulate effectively during a surgical procedure. On the other hand, the fact that the broach or rasp comprises a solid metal body does mean that the broach or rasp is particularly rigid.
In order to reduce the weight and cost associated with the metallic broaches and rasps described above, it has been proposed to manufacture devices using alternative materials. In particular, it has been proposed that instead of metal, a polymer may be used. One example of this is described in U.S. Pat. No. 5,454,815, which describes a bone rasp having a plastic toothed working section with teeth and cutting edges. The rasp is intended to be manufactured inexpensively, making it suitable for one-time use and thereby making cleaning and sterilisation of the used rasp unnecessary. The rasp includes a connecting section for connecting the rasp to an impact tool. Other devices comprised entirely of a polymer have also elsewhere been proposed.
A problem with the non-metallic device described above is that it does not have the same rigidity as the earlier metallic devices. During a surgical procedure involving the removal of bone, a broach or rasp is subjected to a significant amount of stress as it is impacted against the bone. Plastic broaches or rasps are less suited for withstanding these forces and may potentially break or fracture during the procedure. Surgeons are also known to prefer using metallic broaches because they are rigid and do not yield when pressed against the bone to be removed.
Accordingly, there is a need for an alternative approach to reducing the cost and weight of medical devices such as broaches or rasps, in which at least some of the sturdiness and rigidity of earlier solid metal devices may be retained.